This is a multi-center, prospective, randomized, double-blind, parallel, placebo controlled clinical trial evaluating the efficacy of sitagliptin in suppressing glucagon release in subjects with type 1 diabetes over a 16 week treatment period. The hypothesis of this study is that sitagliptin (Januvia™) will decrease post-prandial glucagon release and may result in improved glucose control in adult patients with type 1 diabetes. There is only one small, pilot study of sitagliptin in patients with type 1 diabetes which significantly reduced total daily insulin dose and A1c values while improving mean blood glucose (MBG) and time spent in euglycemic range (1). In the pilot study, GLP-1 and glucagon levels were not assessed. The purpose of this trial is to determine if sitagliptin can suppress the paradoxical rise of glucagon, and thus can decrease A1c.